I run 120 lb/in springs on my Duster and have been happy with them. Full disclosure, my Duster is set up more for AutoX than the summer driving you’re talking about.
That said, I run a large rear sway bar because the 120 lb/in springs are still on the soft side for how my car is set up.
Between the 85 lb/in springs and the 120 lb/in springs I’d run the 120 lb/in springs. They’re probably at the upper end of the spring rate you’d want to run on your car based on your description of its use, but they should be fine.
